On 2022/11/11 20:05, Zeng Heng wrote:
On 2022/11/11 19:31, Jonathan Cameron wrote:
On Thu, 10 Nov 2022 21:26:15 +0800
Zeng Heng <zengheng4@xxxxxxxxxx> wrote:
There is warning reported by kobject lib in kobject_put():
kobject: '(null)' (00000000be81a546): is not initialized, yet
kobject_put() is being called.
WARNING: CPU: 0 PID: 535 at lib/kobject.c:718 kobject_put+0x12c/0x180
Call Trace:
cdev_device_add
__iio_device_register
__devm_iio_device_register
tmp117_probe
If don't need to register chardev for most of IIO devices,
we just register them with device_add() only, and use device_del()
to unregister them.
Otherwise, when device_add() fails in internal and calls kobject_put()
in error handling path, it would report warning because the device
never be registered as chardev and there is no release function for it.
Fixes: 8ebaa3ff1e71 ("iio: core: register chardev only if needed")
Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
Interesting corner case. The cdev_device_add() call is fine with
!dev->devt which is what this code was taking advantage of. The
exception
as you have highlighted is the error path of device_add().
So I think it should also cope with unwinding if device_add() fails
and not be calling cdev_del() Note that cdev_device_del() has the
appropriate guards to be safe whether or not (dev->devt) is true.
Perhaps change cdev_device_add() to have
rc = device_add(dev);
if (rc && dev->devt)
cdev_del(cdev);
return rc;
yes, I agree with your opinion about cdev_device_add(), which would be
more flexible
for callers.
And I *just find* there is existing patch trying to fix this out.
https://lore.kernel.org/lkml/Y1fmgCS7fuf%2FLQBc@xxxxxxxxx/
So just pass the patch.
Best Regards,
Zeng Heng
---
drivers/iio/industrialio-core.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/iio/industrialio-core.c
b/drivers/iio/industrialio-core.c
index 151ff3993354..f4f48bda07f7 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1982,7 +1982,11 @@ int __iio_device_register(struct iio_dev
*indio_dev, struct module *this_mod)
/* assign device groups now; they should be all registered now */
indio_dev->dev.groups = iio_dev_opaque->groups;
- ret = cdev_device_add(&iio_dev_opaque->chrdev, &indio_dev->dev);
+ if (iio_dev_opaque->attached_buffers_cnt ||
iio_dev_opaque->event_interface)
+ ret = cdev_device_add(&iio_dev_opaque->chrdev,
&indio_dev->dev);
+ else
+ ret = device_add(&indio_dev->dev);
+
if (ret < 0)
goto error_unreg_eventset;
@@ -2008,7 +2012,10 @@ void iio_device_unregister(struct iio_dev
*indio_dev)
{
struct iio_dev_opaque *iio_dev_opaque =
to_iio_dev_opaque(indio_dev);
- cdev_device_del(&iio_dev_opaque->chrdev, &indio_dev->dev);
+ if (iio_dev_opaque->chrdev.kobj.state_initialized)
+ cdev_device_del(&iio_dev_opaque->chrdev, &indio_dev->dev);
+ else
+ device_del(&indio_dev->dev);
mutex_lock(&iio_dev_opaque->info_exist_lock);
